Craftable items are cool. They're also rough to make and rough to get pointed to. Finding recps is hard, and sometimes very expensive to buy or acquire. Crafting is not cheap.

When you're capable of making an item, it's considered polite to do so, for the sake of those around in your guild who might need it. Now that we have guild banks, you can drop it in there. Just take a look at the guild tab and see if there's someone around that level to donate to first before selling. Especially in the case of other crafters and patterns/recps/etc. See if that pattern needs to go to a guild crafter first before selling.

When requesting craftable items, it's considered impolite to turn around and sell the item for cash. Your guildies tend to do this out of the goodness of their heart, so it's considered nice to share in the profit if you were to do such a thing. Generally, it's bad form to do otherwise, and will result in your guildies not building you things in the future. ^.^ If the item in question is in the guild bank, this is not allowed at all. No one takes out from the guild bank to sell (or make items to sell) except the Guild leaders, to turn back to the guild money.

Also, usually, when requesting items, it's considered polite to have the mats to give them, or to pay them a little for their time. It's not -expected- for guild mates, but it is nice, or trade them something useful to them if you can't get the mats. For guildies, it's considered impolite to ask for mats, as that's what any crafter can do out in the wild. Just try to be considerate of what it's going to take, and in the case of something soulbound, like Nethers, pay them. Those don't come easy or cheap, no matter where you go.

When out leveling, and you find mat items, stack some of those up in the guild bank, for those who might need. You have extra silk? You have too much iron? A stack is always nice to fill out the tabs. And can later be used to make guild items as discussed above.

Lastly, it's considered impolite to request items for non-guild members (even alts), with the rules in mind above. If a guildie feels they could do so without any trouble, they should, but if it will be difficult, then it's the same as a sale to the open market. And it should be treated as such, with pay and mats and all of that.

So that about covers the "etiquette" for crafting. Give a little, get a little.